Optical flash trigger for EOS-M without built-in flash

I have an EOS-M with a Meikon housing and I am trying to figure out the best way to trigger an external strobe. I got a 90EX speedlite, which works fine to trigger the strobe. It works with the camera's TTL to instruct the Sea & Sea strobe to output the correct power. HOWEVER, it has an annoying auto-off feature: whenever the camera turns off, the strobe shuts down as well.

I can enable the camera screen power down and disable the camera system auto-off, so the camera will stay on the whole dive. However, I would really like to be able to turn off the camera between dives, and not need to open the housing again to turn the 90EX back on.

I was wondering what my options are and if anyone has reccomendations. So far I have considered:

Just open up the housing to turn the flash back on every dive. Works okay, but I'm worried about getting water into the housing when reopening it.

Leave the camera on between dives. Potentially okay, but I battery barely lasts two dives as it is. Maybe I just need a fresh battery?

Find another flash that doesn't auto power off. I've looked at some others, but they seem to also have power-save features that can't be disabled.

Get a dedicated underwater strobe system. TRT-electronics makes one, but it's really expensive. For that price, I could get an EOS-M3 with a built in flash, and a new Meikon housing for it.

Try to add a new bulkhead to the housing to use an electrical flash trigger

Either try to add a new button to the housing to turn the flash on, or solder something on to the flash button and link it to a new button on top of the camera power button so that the power button turns on/off both the camera and flash.

Any recommendations, or other, simpler options that I have overlooked?

I just picked up an ST-E2 canon flash transmitter, which does not turn off, can trigger the flash in manual mode, but it uses a canon specific TTL sync protocol that the Sea and Sea does not respond to properly. So that unfortunately is a no-go.